This invention relates to improvements in an electrostatic separating apparatus by utilizing an induced electrostatic field in an electrically insulating solvent solution.
The separating apparatus for the treatment of sewage or waste liquid utilizing an induced electrostatic field in an electrically insulating solvent solution have been developed by the inventors and disclosed in Japanese Patent Publication No. 15549 of 1965, No. 3941 of 1976, No. 3942 of 1976, No. 23742 of 1976 and No. 22821 of 1989.
These apparatus comprises a tank containing an electrically insulating solvent solution and the tank in which an inlet for feeding the liquid to be treated and an outlet for discharging the treated liquid are provided has a discharge outlet for floated impurity above the upper surface of the solvent solution layer. Additionally, there are arranged, in the solvent solution in the tank, a pair of electrodes between which a high direct current voltage is applied. By this structure, the organic substances contained in the liquid to be treated introduced from the inlet for feeding the liquid are dissolved in the solvent solution by the action of an electrostatic field formed by the pair of electrodes and the floated impurity of the intermediate layer formed on the upper surface of the solvent solution layer is discharged from the discharge outlet for floated impurity and the treated water in the treated liquid layer formed on the upper surface of the intermediate layer is discharged from the outlet for treated liquid.
By using such conventional electrostatic separating apparatus, sewage or waste liquid has been treated in high efficiency and treated water containing low amount of impurity could be discharged. However, incorporation of fine particles of gum insoluble in both of the solvent and water and/or the solvent into the treated water cannot be avoided when the gas dissolved in the liquid to be treated is separated in the electrostatic field and floats. Thus, a secondary treatment is further required to discharge the treated water matching the waste water criteria in many cases. The regulation on the content of organic substance in waste water became more and more stringent recently.
The production and use of Freon solvent detrimental to global environment have been prohibited all over the world and the pollution of underground water with chlorinated solvents also faces to a crisis of global scale.
An object of the invention is to provide a compact electrostatic separating apparatus which can recover the solvent contained in the water polluted by such solvent to 90% or higher by the treatment of the polluted water and further which can remove almost completely the solvent and others remaining in the treated water.